1. Technical Field
The present invention relates to a magnetoelectric heterostructure, which consists of a ferromagnetic layer and a ferroelectric layer with some buffer layers in between. And more particular a magnetoelectric heterostructure with magneto-optic and electro-optic effects. It is also related to a method to fabricate the magnetoelectric heterostructure.
2. Technical Background
Interest in multiferroic materials combining two or more ferroic properties, especially ferroelectric and ferromagnetic properties, has inspired a flurry of research activities in recent years due to a great expectation of potential applications in the microelectronics field. Aside from the applications of both ferroelectric (FE) and ferromagnetic (FM) properties, the magnetoelectrics effect can be used in multiple-state memory elements, in which data is stored both in the electric and the magnetic polarizations, or magnetoelectric signal processing devices, such as an FMR-based phase shifters and filters.
The magnetoelectric (ME) effect is defined as the dielectric polarization of a material in an applied magnetic field or an induced magnetization in an external electric field. The effect, first observed in antiferro-magnetic Cr2O3, is weak in single-phase compounds. Promising single-phase multiferroic materials, such as BiFeO3, TbMnO3, and YMnO3, have been found, and their modified derivatives been extensively investigated. However, there are still very few applicable magnetic ferroelectric materials discovered so far, and their multiferroic effects are not significant enough to be useful in practical applications.
An alternative is to form multiphase complexes, e.g., composites or multilayer structures, in which each phase exhibits a strong ferroic property. To date, in most research, multilayer or bilayer multiferroic structures are laminated and sintered together, or bonded by silver epoxy. In such circumstances, strains and inhomogeneities at the interfaces, or the existence of a foreign layer, complicate the understanding of the important magnetic-electric coupling phenomenon. In contrast, epitaxial multilayer films are more desirable for both theoretical studies and potential applications since there are many factors such as layer thickness and interfacial roughness that may be accurately controlled.
On the other hand, both magneto-optic (MO) and electro-optic (EO) effects are widely used in optical industry. Current photonic integrated circuits (PICs) are based on either polymer or SiO2 films that are limited in device functionality. Electro-optic or magneto-optic materials are very attractive in adding functionality and adaptivity to PICs. However, very limited work has been done on PICs with functional materials. In this invention, we have developed a multifunctional thin film structure with MO and EO effects, which would enable the integration of MO isolators with other monolithic optical devices, such as lasers, waveguides, modulators, and detectors.